can be an important factor for the movement of canopy and understory
species. A discontinuous canopy may act as a barrier for species that need
cover from predators or for arboreal species that move mainly through upper
forest strata.
Some corridors may be bisected by roads or rivers, which can be a barrier
to animal movements. In tropical forests, even narrow road and powerline
clearings (less than 80 m wide) can significantly impede movements by sensi-
tive understory birds (Laurance 2001), small mammals (Goosem and Marsh
1997; Goosem 2000), and arboreal marsupials (Wilson 2002). Therefore,
such habitat discontinuities should be avoided where possible by facilitating
wildlife movement via replanting gaps and structural corridors such as high-
way underpasses.
Agroforestry Corridors and the Wildlife at Risk
Agroforestry systems may not be effective corridors for all wildlife. There are
two groups that will need special attention. The first is rainforest specialists
that avoid disturbed habitat. In two comparative studies of complex agro-
forests and primary forests, for example, the bird species that were not
detected in agroforests were the large, understory, or terrestrial insectivores
(Thiollay 1995; Greenberg et al. 1997). Therefore, these species must become
one of the target groups for future research and monitoring because they are
sensitive to extinction in fragmented landscapes, even in the presence of agro-
forestry corridors.
The second wildlife group at risk is game and large predator species. Agro-
forestry corridors could become critical population sinks for game and predator
species that are actively hunted for food, for income, or to protect domestic ani-
mals (see Chapters 13 and 14, this volume). On central Amazon farms, for
example, large predators such as jaguars and harpy eagles often are attracted to
domestic animals and are therefore killed by farmers (S. G. Laurance, pers. obs.).
Conclusions
It has been 25 years since wildlife corridors were first suggested as a means to
mitigate the effects of habitat fragmentation. Despite a rapidly increasing
body of research on corridors, for some scientists there is still too little infor-
mation available to justify the inclusion of corridors in regional conservation
strategies. Yet natural forested areas are diminishing in size, and as a result
there are fewer opportunities to acquire or protect remnant habitats that can
maintain habitat connectivity. Under these circumstances a wait-and-see
approach could be disastrous. Acting now to protect and establish wildlife cor-
ridors might entail some risks, but it will be far easier to remove a corridor in
the future than to create one where the original habitat has been destroyed.
- Landscape Connectivity and Biological Corridors 59